linux-kernel - Re: [RFT][PATCH 0/3] cpufreq / PM: QoS: Introduce frequency QoS and use it in cpufreq

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Message-ID: <20191017095942.GF8978@bogus>
Date:   Thu, 17 Oct 2019 10:59:42 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Osipenko <digetx@...il.com>
Subject: Re: [RFT][PATCH 0/3] cpufreq / PM: QoS: Introduce frequency QoS and
 use it in cpufreq

On Thu, Oct 17, 2019 at 03:27:25PM +0530, Viresh Kumar wrote:
> On 16-10-19, 15:23, Sudeep Holla wrote:
> > Thanks for the spinning these patches so quickly.
> >
> > I did give it a spin, but unfortunately it doesn't fix the bug I reported.
> > So I looked at my bug report in detail and looks like the cpufreq_driver
> > variable is set to NULL at that point and it fails to dereference it
> > while trying to execute:
> > 	ret = cpufreq_driver->verify(new_policy);
> > (Hint verify is at offset 0x1c/28)
> >
> > So I suspect some race as this platform with bL switcher tries to
> > unregister and re-register the cpufreq driver during the boot.
> >
> > I need to spend more time on this as reverting the initial PM QoS patch
> > to cpufreq.c makes the issue disappear.
>
> Is this easily reproducible ? cpufreq_driver == NULL shouldn't be the case, it
> get updated only once while registering/unregistering cpufreq drivers. That is
> the last thing which can go wrong from my point of view :)
>

Yes, if I boot my TC2 with bL switcher enabled, it always crashes on boot.

--
Regards,
Sudeep